Several properties of the LM unit extracted with sodium dodecyl sulfate from Rhodopseudomonas sphaeroides purified reaction centers

Abstract

We describe several characteristics of an LM unit extracted from purified wild-type Rhodopseudomonas sphaeroides reaction centers after treatment with SDS and lauryldimethylamine N-oxide. We also studied another preparation called RC-SDS in which after a similar detergent treatment the H-chain was not separated from the LM unit. The spectral properties of both preparations were similar to those of intact reaction centers; the main differences were a blue shift of the P-865 Q y band and a narrowing of the bacteriopheophytin Q x band. Studies of absorbance changes after steady light or flash illumination showed that LM was depleted of the primary electron acceptor Q I and of the transition metal (Mn), but was still able to react with quinones, with a partial restoration of the photochemistry. The primary acceptor Q 10 was still partly present in RC-SDS and formed in the light a very unstable semiquinone anion. In both preparations, in the presence of added quinones, the flash-induced P-865 + decayed in the dark with multiexponential kinetics, the apparent half-times ranging between 60 ms and 100 s. This recovery was accelerated either by the absence of O 2 or (in the case of LM only) by o-phenanthroline, which also decreased the amplitude of the P-865 + signal. From these experiments it was concluded that in these preparations the site of binding of the secondary quinone Q II was damaged or absent; the altered properties of this LM unit were considered to result from the denaturing action of the detergents, rather than from the absence of the H polypeptide.